In a conventional gas combustion type driving tool, when a contact arm is pressed against a workpiece into which nails are driven, a combustion chamber is closed and fuel is injected into the combustion chamber. Then, when a trigger lever is pulled, mixed gas is ignited and burned. By a pressure of a combustion gas explosively burning, a piston is driven. Therefore, by a driver integrally connected to the piston, a nail is driven into the workpiece. In this combustion type driving tool, each time a driving motion is executed, the trigger lever must be operated being pulled. Therefore, a working efficiency can not be enhanced. In order to solve the above problems, a driving tool is proposed in which nails can be continuously driven when the contact arm is pressed against the workpiece while the trigger lever is being pulled. Concerning this tool, for example, refer to JP-A-2004-074296. In this tool, when the contact arm is pressed against the workpiece while the trigger lever is being pulled, the mixed gas is ignited and the piston is driven.
However, in the gas combustion type driving tool disclosed in JP-A-2004-074296, a combustion frame (which corresponds to a movable sleeve of embodiments of the present application) is connected to a push lever (which corresponds to a contact arm of the embodiments of the present application). When the push lever is pressed against the workpiece, the combustion frame is raised and the combustion chamber is closed. Therefore, although it is possible to continuously drive the nails, after the push lever has been pressed against the workpiece, various preparations must be made such as a closure of the combustion chamber, an injection of the fuel gas and a generation of the mixed gas. Therefore, it is always necessary to take a preparation time after the push lever has been pressed against the workpiece. Further, in order to open the combustion chamber, it is necessary to release the push lever from the workpiece each time the combustion chamber is opened. Therefore, although the nails can be continuously driven, much time is required for the preparation work to ignite the mixed gas.